Thank you very much for your help, Janett.
The method you proposed is an "object oriented" way (first include the controller class, and then instantiate it and create a new object). It'll work, sure.
But... there are not any "prestashop method" for this? Using context object, or maybe some Prestashop classes? I have been searching forums, and they talk about using "$this->getController('nameOfController')" at the module, but it doesn't work, I don't know if this worked in some previous Prestashop version, and they moved the method to another class in more recent versions.